In general, a photographic material is produced by coating at least one photographic layer on a plastic film support. As the plastic film for a photographic support, a cellulosic polymer such as typically triacetyl cellulose (hereinafter referred to as "TAC") and a polyester polymer such as typically polyethylene terephthalate (hereinafter referred to as "PET") are generally employed. Recently, the use of polyethylene naphthalate having higher heat resistance than PET as a photographic support has been investigated.
A photographic material is generally grouped into one of two groups: one being in the form of a sheet film such as an X-ray film, a film for photomechanical processes and a cut film, and the other being in the form of a roll film such as typically a color or black-and-white negative film having a width of 35 m/m or less. The latter is generally housed in a patrone (cartridge) and is charged in a camera for picture-taking.
As a support for a roll film, heretofore, TAC has been used essentially. The characteristics of TAC film as a photographic support are that TAC has no optical anisotropy and has a high transparency and that TAC has an excellent property of easily smoothing the curl of a developed photographic material having it as a support. The excellent property of TAC of easily smoothing the curl of a developed photographic material having it as a support results from the molecular structure of the TAC film itself. Specifically, since a TAC film has a relatively high water-absorbing property, though being a plastic film, because of its characteristic molecular structure, the molecular chain of the film comes to be fluid after the support film of TAC has absorbed water during development of a curled roll film so that the curl of a long-time stored roll film may be smoothed by rearrangement of the molecular chain as fixed in the long-time stored and curled roll film.
If a photographic material having a film support not having an uncurling property is used as a roll film, it would involve problems of having scratches and out-of-focusing during the printing step of forming an image on a photographic paper from the developed roll film and also a problem of jamming during feeding of the roll film.
The use of photographic materials has been diversified widely in these days, and the technology for rapid feeding of a photographic film in a camera or the like during picture-taking with it, elevation of the image magnification and reduction of the size of picture-taking devices has advanced noticeably. Under the advanced technology, the support of photographic materials is needed to have high strength and high dimension stability and to be thin as much as possible.
Since a TAC film has a rigid molecular structure, the film quality of it is brittle. Therefore, at present, use of the film involves various difficult problems.
As opposed to a TAC film, a polyester film has excellent producibility, mechanical strength and dimension stability. Therefore, it has heretofore been considered that such a polyester film would be substitutable for a TAC film.
Since a polyester film strongly curls and the curl of the film remains much when it is rolled, handling of a developed photographic material having a support of the film is troublesome. Therefore, despite the above-mentioned excellent properties, use of the film as a support for a roll film was unfavorable. As a means of overcoming the curling property of the film, U.S. Pat. No. 4,141,735 has proposed heat treatment of the film for reducing the curl of the film. However, if a bulk roll of the film is simply heated on an industrial scale, it would be shrunk, spotted or wrinkled to cause unevenness of an emulsion layer to be coated thereover. Because of this reason, such a heat-treated bulk roll of the film could not be put to practical use.